The invention relates to a winding mechanism for a sun screen which is stretched in the form of a tunnel during use, which winding mechanism is intended for use in an open roof construction of a vehicle and which comprises a winding tube which is rotatable about an axis of rotation for winding and unwinding said sun screen.
When such a sun screen is used in a vehicle, and it is desired to utilize the interior space of the vehicle optimally, the sun screen should extend as closely to the roof liner of the vehicle in question as possible over its entire width. Since the inside contour of the roof liner of a vehicle is generally curved (in particular seen in a plane perpendicularly to the longitudinal axis, front to back, of the vehicle), also the sun screen will be curved in this manner, or, in other words, extend in the form of a tunnel. Such a curvature can be realised, for example, by using curved, stationary guides extending in the transverse direction of the vehicle.
One drawback of a sun screen which is thus stretched in the form of a tunnel is the fact that some parts of the sun screen (in particular the central part thereof) are stretched during winding and unwinding of the sun screen, while other parts (in particular the edge areas) are not stretched, so that they can flap uncontrollably.
It is an object of the present invention to provide a winding mechanism of the type to which the invention relates, by means of which the above-mentioned drawback can be eliminated in a simple yet effective manner.
In order to accomplish that objective, the winding mechanism includes a guide for the sun screen disposed beside the winding tube, which guide is curved in such a manner that the distance via the guide and via the surface of the winding tube surface to a line on the surface of the winding tube that extends parallel to the axis of rotation is the same for all points that are located at the same longitudinal position on the sun screen.
The phrase xe2x80x9cpoints located at the same longitudinal position on the sun screenxe2x80x9d is understood to mean those points on the sun screen which are located on the line of intersection between a vertical plane extending transversely to the vehicle and the sun screen. Said line will be curved to conform to the tunnel form of the sun screen. Starting from a random point on said line, the distance (seen in the longitudinal direction of the sun screen) via said guide and via said winding tube surface to a line (in principle any line) on the surface of the winding tube that extends parallel to the axis of rotation will be the same in all cases. In this manner, every part of the sun screen will be stretched in the same manner, so that flapping of the sun screen will not occur. Thus the curved guide provides compensation for differences in length from the sun screen, which is stretched in the form of a tunnel, to the winding tube for said sun screen.
When the sun screen extends directly from the thus curved guide to the winding tube surface, the sun screen will make contact with the winding tube at different circumferential positions along the length thereof. Put differently, different parts of the sun screen will be wound onto the winding tube over different lengths before reaching the aforesaid line that extends parallel to the axis of rotation. A direct consequence of this is that the various parts of the sun screen (seen in the transverse direction of the sun screen) make contact with the winding tube at different angles. This may affect the correct winding and unwinding of the sun screen, while the sun screen is moreover subjected to possibly harmful deformations.
In order to overcome this drawback, it is proposed in accordance with a preferred embodiment of the winding mechanism according to the invention to dispose a rectilinear auxiliary guide between said guide and said winding tube, in such a manner that the sun screen will make contact therewith over preferably the entire width of the sun screen.
Since the sun screen is in contact with the auxiliary guide over its width, it is ensured that said sun screen will make contact with the winding tube at the same angle, and consequently at the same location, seen in a circumferential direction, over its entire width. In other words, the sun screen will arrive at the winding tube in a flat condition.
Such a rectilinear auxiliary guide can be realised in various ways. Thus the auxiliary guide may be a rod having a small diameter in comparison with the winding tube. In principle, the same problem occurs when such a rod-shaped auxiliary guide is used as that which manifests itself at the location of a winding tube if an auxiliary guide is not used, but as a result of the small diameter, the effect that occurs at the location of the auxiliary guide only manifests itself to a very small extent. After all, also in the case of relatively large differences in the angle at which different parts of the sun screen reach the auxiliary guide, the circumferential distances between the various angular positions at which different parts of the sun screen reach the auxiliary guide will be very small.
According to another variant, the auxiliary guide is made up of a gap in a housing, which accommodates the winding tube. Generally, the winding tube of a winding mechanism to which the invention relates will be accommodated in such a housing. A gap formed in the housing can now advantageously perform the function of an auxiliary guide, so that one gap edge guides the sun screen.
The curved guide, but also the auxiliary guide, may be a rotating guide, which may consist, for example, of a large number of cylindrical rollers arranged in side-by-side relationship. The amount of friction with the sun screen, and consequently the wear thereon, can thus be reduced.